Various power line monitored sensors have been disclosed in the prior art. For example, see U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810 and 4,268,818. It has been proposed to use sensors of this type and of the greatly improved form disclosed in the above-identified Stillwel and Fernandes application for dynamic line rating of electrical power transmission lines. See for example, papers numbered 82 SM 377-0 and 82 SM 378-8 entitled DYNAMIC THERMAL LINE RATINGS, PART I, DYNAMIC AMPACITY RATING ALGORITHM; and, DYNAMIC THERMAL LINE RATINGS, PART II, CONDUCTOR TEMPERATURE SENSOR AND LABORATORY FIELD TEST EVALUATION; papers presented at the Institute of Electrical and Electronic Engineers P.E.S. 1982 summer meeting. These papers are incorporated herein by reference. However, the full potential of this new technology has not been realized.
Today, for control and protection, power supply to and from an electrical substation over various transmission lines is monitored by separates devices (current transformers, potential transformers and reactive power transducers) for measuring electrical potential, power factor and current in the conductors of the transmission line and the conductors connected to substation power transformers. These measurements are transmitted in analog fashion by various wires to a central console at the substation where their values may or may not be digitized and sent to a central station for control of the entire power system. The wiring of these devices is difficult and expensive, and every excess wire in a substation presents an additional electrical shock hazard or an induction point for electromagnetic interference on protection/telemetry circuits. Furthermore, when a failure occurs, these sensor lines may be abruptly raised to higher voltages, thus increasing the possibility of shock and failure in the measurement system.
The high cost of capital, uncertain power utility load growth trends, coupled with increasing constraints in acquiring and licensing new facilities including right-of-way for transmission lines make greater use of existing power delivery facilities (remote generating stations, the EHV bulk power network, subtransmission and distribution facilities) a paramount consideration. With deferrals that have occurred in new generation and power transmission facilities, all elements of the power system will be strained to a greater degree than in the past. In order to maintain current reliability levels under these conditions, additional real-time monitoring will be required to assist the dispatch operator and other bulk network functions conducted through a modern Power Control Center.
Some of the functions in a hierarchical modern Power Control Center, operating through Regional Control Centers down to the distribution level, that require a real-time Supervisory Control and Data Acquisition System are as follows:
1. State Estimation PA1 2. On-Line Load Flow Detection PA1 3. Optimum Power Flow Control for Real and Reactive Power Dispatch PA1 4. Security (i.e. Stability) Constrained Economic Dispatch PA1 5. Contingency Analysis PA1 6. Automatic Generation Control and Minimum Area Control Error PA1 7. Dynamic System Security Analysis PA1 8. Energy Interchange Billing PA1 9. System Restoration After an Emergency PA1 10. Load Shedding and Generation Redispatch PA1 11. Determination of Effects of Voltage Reduction and Real and Reactive Power PA1 12. Synchronization of System Load Profiles to validate various computer models and to provide snap shots of maximum, minimum loads, peak day real and reactive powers on lines and equipment PA1 13. Maintain Power Delivery Quality Including Harmonic Content for Critical Loads and Power Factor PA1 14. Limit checking of voltage, line thermal loadings and rate of change under contingency conditions PA1 15. Protective Relaying. PA1 Line and Transformer Bank or Bus Power (MW) Flows PA1 Line and Transformer Bank or Bus Reactive Power (MVAR) PA1 Flow PA1 Branch Currents (I), Bus Voltage and Phase Angles PA1 Bus MW and MVAR Injections PA1 Energy (MWh) and Reactive Energy (MVAR-h) PA1 Circuit Breaker Status PA1 Manual Switch Positions PA1 Tap Changer Positions PA1 Frequency (f) PA1 Protective Relaying (Differential Currents, etc.) PA1 Operation PA1 Power Line Dynamic Ratings Based on Conductor Thermal PA1 (Temperature) Limits or Sag PA1 Ambient Temperature/Wind Speed PA1 Line and Equipment Power Factors PA1 Sequence-of-Events Monitoring PA1 Line Voltage PA1 Power Factor or Phase Angle PA1 Power Per Phase PA1 Line Current PA1 Reactive Power Per Phase PA1 Conductor Temperature PA1 Ambient Temperature PA1 Wind Speed PA1 Harmonic Currents PA1 Frequency PA1 MW-h and MVAR-h (processed quantities) PA1 Profiles of above quantities from stored values
The key parameters that require measurement for a modern Power Control Center State Estimator and On-Line Load Flow that provide the input data base for the various functions listed above are:
One of the major problems in implementing a modern Power Control System is to add instrumentation throughout the bulk transmission network at Extra High Voltage (up to 765 kV) line voltages and at distribution substations and feeders. This must be done without disrupting existing operations of equipment and facilities that are largely in place. Another requirement is to avoid adding too many transducers that might alter the burden on existing current transformers and degrade accuracy of existing metering or relaying instrumentation.
The toroidal conductor State Estimator Module and ground station processor, receiver/transmitter of the present invention eliminates the necessity for multiple wiring of transducers required with conventional current and potential transformers and collects all the data required from lines and station buses with a compact system. The invention results in significant investment, installation labor and time savings. It completely eliminates the need for multiple transducers, hard-wiring to current transformers and potential transformers and any degrading effects on existing relaying or metering links. The system can be retrofitted on existing lines or stations or new installations with equal ease and measures:
The state-estimator data collection system described in this application enables power utilities to implement modern power control systems more rapidly, at lower cost and with considerable flexibility, since the devices can be moved around using hot-sticks without having to interrupt power flow. The devices can be calibrated and checked through the radio link and the digital output can be multiplexed with other station data to a central processor via remote communication link.
Many problems had to be overcome to provide an electrically isolated state estimator module that can be hot stick mounted to energized conductors including the highest used in electrical transmission.
Among these were: The design of a positive acting mechanism for hinging the two parts of the module and securely clamping and unclamping them about a live conductor while they were supported by a hot stick. Measurement of the voltage of the conductor in a self-contained electrically isolated module. The desire to make many electrical measurements with a necessarily small and light module and common utilization of a single radio channel by the up to 15 modules which might be required at a single substation.
Such hot stick activated hinge and clamp mechanisms do not exist in the prior art. The voltage transformers and capacitive dividers of the prior art are not electrically isolated. Separate measurements of all electrical quantities desired wound require too much apparatus in the module. Synchronization of module transmissions would require a radio receiver in each module.